This invention relates generally to the field of spinal fusion surgery and more specifically to interspinous fusion implants and bone growth stimulation systems.
In 1986, the first interspinous device was introduced in Europe. It was the first dynamic stabilization system and consequently has the longest history at present. The device's original design was a titanium blocker that was inserted between adjacent processes and held in place with a polyester band wrapped around the spinous process above and below the blocker. After this first-generation device showed positive results, a second generation of interspinous implants were developed. The primary change was in the material used for the interspinous spacer. It was changed from titanium to polyetheretherketone (PEEK), a strong, plastic-like polymer that has more elasticity and is therefore less rigid than the previously used material. The implant has notches that fit the physiological shape of the lumbar spine.
Several devices currently exist that can be inserted between the spinous apophysis. Said devices have their antecedents in bone grafts placed between the spines more than fifty years ago. They were H-shaped and placed so that their ends surrounded the spines and their horizontal part was located between said spines in order to diminish the mobility among the vertebrae and achieve its final fusion. Likewise, there exist antecedents related to vertebral fusion which used different bow types, mostly metal bows to be linked to the spinous apophysis so that they become immobilized.
Newer technologies also exist that prohibit both flexion and compression between successive spinous processes. These devices are inserted between the spinous processes and contain barrel-like objects that maintain a space between the spinous processes thus prohibiting compression, while also containing successive plates with spikes that bore into successive spinal processes thus prohibiting flexion.
The problem with all of the known devices is their limited ability to adapt to the unique contours of each individual spinous process of each individual patient. This leads to reduction in the useful life of the implant after implantation and earlier failure than can be accomplished with an implant that adapts to the contours of the spinous between which it is implanted. This is important, because interspinous implants are meant to be long-term solutions that remain implanted for preferably the life of the subject who is treated with them. With life expectancy of people in developed countries exceeding 80 years of age and many people now living actively into their 90 s, these devices must maintain their functional integrity and must not fail for decades. Unfortunately, many of the current implants are prone to failure due to their inability to adapt to the shape of the specific spinous processes of the individual. What is needed are implants that adapt to the specific contours of each spinous process with which they are in contact, and that therefore remain firmly in place and maintain their functional integrity and are unlikely to suffer a mechanical failure for the life of the recipient of the implants.
Yet another problem is that most implants that prohibit compression and flexion require set screws and drivers to fix the components of the implants to the bone and fix the parts of the implant firmly in place relative to one another. This requires extra space to work in order to screw and unscrew. In addition, the single point of a set screw is tasked with maintaining the orientation of the parts of the device for as long as the device is in the body. All of the forces that pull and push the parts of the device toward and away from one another converge on the single set screw point that is tasked with maintaining the functional integrity of the device and prevent its failure. What is needed are devices that remain their functional integrity for long periods of time and are not prone to the limitations of using set screws.